Categorizing a prognostic variable: review of methods, code for easy implementation and applications to decision-making about cancer treatments

Stat Med. 2000 Jan 15;19(1):113-32. doi: 10.1002/(sici)1097-0258(20000115)19:1<113::aid-sim245>;2-o.


Categorizing prognostic variables is essential for their use in clinical decision-making. Often a single cutpoint that stratifies patients into high-risk and low-risk categories is sought. These categories may be used for making treatment recommendations, determining study eligibility, or to control for varying patient prognoses in the design of a clinical trial. Methods used to categorize variables include: biological determination (most desirable but often unavailable); arbitrary selection of a cutpoint at the median value; graphical examination of the data for a threshold effect; and exploration of all observed values for the one which best separates the risk groups according to a chi-squared test. The last method, called the minimum p-value approach, involves multiple testing which inflates the type I error rates. Several methods for adjusting the inflated p-values have been proposed but remain infrequently used. Exploratory methods for categorization and the minimum p-value approach with its various p-value corrections are reviewed, and code for their easy implementation is provided. The combined use of these methods is recommended, and demonstrated in the context of two cancer-related examples which highlight a variety of the issues involved in the categorization of prognostic variables.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antineoplastic Agents / administration & dosage
  • Chi-Square Distribution
  • Humans
  • Lymphoma / drug therapy
  • Male
  • Models, Statistical*
  • Neoplasms / therapy*
  • Probability*
  • Prognosis*
  • Retrospective Studies
  • Risk
  • Seminoma / drug therapy
  • Seminoma / radiotherapy
  • Seminoma / surgery
  • Survival Analysis
  • Testicular Neoplasms / drug therapy
  • Testicular Neoplasms / radiotherapy
  • Testicular Neoplasms / surgery
  • Tomography, X-Ray Computed
  • Treatment Outcome


  • Antineoplastic Agents